The optical system of typical electronic cameras such as widely used video cameras and digital still cameras include imaging optics, IR cut filters, optical low pass filters, and imaging devices such as Charge Coupled Devices (CCD) and Complementary Metal Oxide Semiconductors (CMOS). These are arranged in the order set forth along the optical axis starting from the side of a photographic subject (see, for example, patent document 1).
These imaging devices have sensitive properties of being responsive to light radiation in a wavelength band that is wider than the wavelength band of visible radiation detectable by the human eye (the visible spectrum). Thus, the imaging devices are responsive to light radiation in the infrared spectrum in addition to the visible spectrum.
Specifically, the human eye responds to light radiation in a wavelength range from approximately 400 nm to 620 nm in dark locations and to light radiation in a wavelength range from 420 nm to 700 nm in bright locations. In contrast, for example, a CCD responds to light radiation beyond a wavelength of 700 nm in addition to light radiation in the wavelength range from 400 nm to 700 nm.
In view of this, an imaging device, as disclosed in patent document 1, uses an IR cut filter in addition to a CCD as an imaging device so as to prevent light radiation in the infrared spectrum from reaching the imaging device, in an attempt to obtain images as close to those perceived by the human eye as possible.